Your sleep goes through various stages. 

The first is called non-rapid eye movement (NREM) sleep. During this stage, your brain waves slow down considerably. After an hour or two of this sleep, your brain activity picks up for the second stage – rapid eye movement (REM). Most of our dreams occur during REM sleep. 

You will typically cycle these stages between four to six times a night, changing from NREM to REM sleep and back again every 70 to 120 minutes. However, if the process is interrupted you may have a sleep disorder.  

If you are suspected of having a sleep-related disorder, your doctor is likely to suggest you undergo an overnight sleep study or polysomnography (PSG). This study will determine if and why your sleep patterns are being interrupted.^1,2

A PSG involves several simultaneously conducted observations and tests (some using electrodes attached to various parts of the body) that monitor:  
 

• chest and stomach movement  
• airflow at the nose and mouth  
• sleeping positions 
• oxygen saturation (measured through a pulse oximeter attached to your finger or earlobe) 
• brain activity (an electroencephalogram) 
• muscle movement (electromyogram) 
• heart activity (electrocardiogram) 
• eye movements (electrooculogram).